"AlreadyPettedLabel": "Has already been petted",
"NeedsToBePettedLabel": "Needs to be petted"

and you'll see the new labels in game.

Credits:

The initial idea for this was inspired by Orspeeder's Chest Label System mod. Also, thank you to Legiion/TheCatMan of NPC Gift Taste Helper for helping Jinxie gain a better understanding of using custom assets.